A common problem encountered by freight haul tractor trailers, as well as smaller trailers used for non-commercial purposes such as recreational trailers, is the loosening of the lug nuts on the wheels of the trailer.
A common problem results from methods used to secure nuts to lug bolts on new truck and trailer wheels. Unless properly addressed “seating-in” during initial use can result in a reduction of the clamp force, and thereby the torque, which holds the wheel to the axle hub. This can over time create a gap between the nut and the wheel which enables the initially tight nuts to loosen up.
Further, the stacking of components on a vehicle wheel hub creates a cumulative thickness of the stacked parts. The initial torque can force the material of the stacked components to yield, thereby allowing the nuts to loosen by “bleeding off” the initial torque and preload, again, causing the nut to loosen.
Loss of torque can also occur as a result of long storage periods where the wheel assembly is subjected to repeated cycles of heating and cooling.
Once the nuts have loosened, the wheel is able to rock and wobble back and forth on the lug bolts. After a period of time, the lug hole diameter in the wheel can be significantly enlarged, damaging the wheel as well as severely degrading the stability of the trailer, rending it uncontrollable. Also, relative movement of the wheel can result in fatigue failure of the lug bolts, causing catastrophic separation of the wheel from the axle hub. For example, in an emergency or panic stop, once loosened under hard application of the brakes the wheel can shear off the lug bolts, thus rendering the trailer or vehicle uncontrollable. Once detached the wheel can become a dangerous projectile as well, capable of seriously injuring others.
This situation can be further aggravated by the accumulation of debris on the various engaged, load bearing surfaces of the lug nut system.
Representative of the art is U.S. Pat. No. 6,592,314 which discloses a wheel nut and washer assembly for securing a wheel to a motor vehicle axle. The wheel nut includes a body having a longitudinal axis, the nut body also having an axial threaded aperture and a pair of ends, one end being in the form of a smooth steel external surface. The wheel nut also includes a steel washer having an end terminating in a smooth annular surface in surface-to-surface engagement with the body end thereby maintaining axially alignment of the body and washer enabling relative movement of said body and washer about said axis. A decorative cap on the assembly is configured so that it holds the washer on the nut, a gap between the cap and washer to enable the washer to freely rotate and move laterally relative to the nut.
What is needed is a swivel nut having a ridge and groove snap-on torque cone. The present invention meets this need.